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WHAT IS A CAN-BUS
ELECTRICAL SYSTEM
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Can-Bus is a method of hardware and software to enable communications between electrical and electronic things on your vehicle. These things can also be electro-mechanical.  CAN-BUS stands for Controller Area Network and the 'Bus' part is explained later herein. The Harley-Davidson is now well into the new century with a much more advanced motorcycle. The engine is controlled by the ECM (Engine Control Module) and the overall motorcycle from the headlight, the speakers and the taillights are controlled by the BCM (Body Control Module). Those who mess with the electrical system by installing cheap accessories not designed for Can-Bus will see the error of their ways in short order with fault readouts appearing on the dash display and eventually the possibility of failed systems.

BMW Motorcycle decided to reduce the number of electrical wires and connections and hopefully reduce electrical problems by operating just about everything, to the extent possible, by using digital electronics. There are some definite advantages such as weight saving, manufacturing labor and the potential for much higher reliability as only two wires are needed for most anything. In addition and more importantly the ability for the computer(s) to monitor and talk to each other for just about any function in a very short time period. There are other reasons for going to something like Can-bus. Vehicles are becoming vastly more complicated so more and more computers or mini-computer elements are needed to monitor, produce or accept information from each other.

Example:  In the Classic K bikes there is a single pricey and complicated turn signal flasher and lamp bulb monitoring box. With Can-Bus it could be simplified to incorporate most of its functions and parts in a vastly smaller size into the main computer and even more functions could be added. It could be less costly and more reliable. ABS functions which could incorporate traction control, etc. could be simplified. Traction control and ABS require fairly fast information processing and electronics is absolutely necessary for proper operation.

The problem that arises from Can-Bus is that the electrical system is to some degree no longer relatively easy to modify with changes, darkles (sparkle accessories), add-ons, etc.  Just adding an electrical outlet jack for a phone charger might cause problems. Typically the owners' answer to this is to wire accessory goodies directly to the battery.

Borsch invented Can-bus in the eighties and it is no longer, or never was, a totally German thing.  Your car, if manufactured since the late seventies or so likely has a version of Can-Bus called "OBD" and it is standard now for all cars, the latest version is OBD-II.  OBD stands for On- Board- Diagnostics.  On modern cars a technician can connect a 'reader' (or other more sophisticated gadget) to an electrical plug in your car.  He can read out problem codes as well as non-problem codes. He can get a lot of information about the engine, transmission, brakes, cooling system and much more about the entire vehicle. All this comes from your car's computer(s) and with some types of "readers" he can actually make adjustments and incorporate updates. Updating the vehicle computer(s) is called flashing as the information is transferred to something akin to the BIOS chip in your home computer. Many times a manufacturer will offer updates to correct some problem or other. These updates are obtainable from authorized repair centers.

The various Governments, United States included, have mandated methods of computer readouts in your vehicle.  Our Federal Government mandated that the USA comply with the International Standards for OBD and Can-Bus, which are closely related and probably happened in1994. It was TEN years before BMW put this latest Can-Bus stuff into its motorcycles.  Prior to that BMW had its own versions of OBD incorporated into such as the Extrinsic and early Motronic systems and it was primarily for error codes although there were some outputs and inputs and you'd need the fancy BMW dealership machine ($18,000.00 was a widely discussed number) to do everything.

The Buss (Bus), here is somewhat simplified. A pathway that connects devices, enabling them to communicate. An electrical bus is a common interconnection area point and/or method of transportation of information or electricity per se. a pathway that connects devices, enabling them to communicate. It was used in large trucks and particularly in airplanes since the thirties, maybe before. In that type of usage a bus was typically just a multiple connection point or perhaps a strip of metal with many connections to it for a group of common-connected wires. There might have been more than one such bus with an interconnection switch, usually a circuit breaker, allowing them to be separated or tied together in parallel.

This bus idea is used in your home with multiple connections in the power-meter box for grounds, hot wires and in some cases the neutral. This is a very simplified use of the term of bus and it gets very much more complicated with the usage and meaning today. A vehicle bus carries a lot of people so many think that the word was adopted for electrical signals multiple uses on a single wire. In actuality the word goes way back when buss was spelled with double ss.

In a way, kind of exaggerated, one could think of your TV cable company's single coaxial cable wire coming into your home as a bus carrying all those differing TV and audio programs on just two wires (inner solid wire and the shielding around it). So, warping the use of the term, that could be a signal bus wire. In your vehicles electrical system any particular BUS (there may be more than one) might be just one or two wires carrying all sorts of digital code from many devices connected only to those two wires. Digital coding (which is TIME related) separates the functions.

To spell this out a bit differently a digital bus allows multiple packets of information from different sources to travel down one path simultaneously. Keeping with the analogies the INTERNET is really a bus type system as information travels in packets the same as your E-mail is broken up into many packets. It's the same for web sites, etc. transmitted over the Internet. This is all somewhat of a simplification of what is going on but close to reality.

The more recently a car or motorcycle was designed and built, in general, the more computerized items and numerous 'mini' computers are used to provide many functions. Generally one main computer runs and monitors everything with some peripheral small computers doing specific things that are not capable from within the main computer. The trend for a long time has been to greatly increase the number of small computers in a car. In recent years this has caused innumerable problems with respect to cost so nowadays the trend is to use less individual computers by expanding the main computer functions and abilities.

The first bike to have Can-Bus was probably the Ducati 999 back in 2002. BMW started it with the R1200 in 2004.

Can-Bus allows most of the various computers and peripherals to talk or communicate with each other in both a simplified and complex manner. This means that nearly every electrical device on your bike could be connected to the Can-bus system which continuously and rapidly monitors everything via a computer. The system can also monitor current flow, voltage, etc. If you tried to tap into the electrical system for an extra electrical gadget Can-bus might complain in essence and the Can-Bus computer thinks, rightly or wrongly, that the bike has a problem. It might even record the problem and give you a visual signal that all was not well. If the load was egregious enough the bike might not start or otherwise not able to be ridden.

Some ABS systems talk back and forth with the computer that runs the engine itself.  It is possible for the ABS to monitor acceleration or other speed conditions or events and then with other inputs the bike might have traction control applied. That is already done on cars and a few bikes and will be appearing on more bikes in the future.

Problems with Can-Bus as far as vehicle owners are concerned is that we cannot just willy-nilly connect up electrical gadgets or easily modify the electrical system.  We also are more likely to be needing a dealership to read codes and find problems with fancy expensive test equipment because when the bike stops running we will be much less likely to be able to fix it ourselves. Note that it is entirely possible that the systems will be so reliable that many electrical problems seen in the past will be eliminated. So far, the record tends to show an increased reliability. That is to be expected especially when the vehicle is new or nearly new.

(Reprint) For now, the primary method of adding farkles, etc. to Can-bus bikes will be connections directly to the battery. However, messing with the stock lighting systems is not for the amateur. In fact, there are already some small companies making an attempt to sell headlight accessories that don't meet their advertising claims and interfere with operation. This is one area where design absolutely requires true electrical engineering expertise. It's a case of buyer beware.

Additional information can be found here.
© Copyright, 2011, R. Fleischer

 

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